Aerial passenger tramway



Dec. 2, 1941. w E Z I AERIAL PASSENGER TRAMWAY Filed Feb. 18, 1939 2Sheets-Sheet 1 if} 2' INVENTOR Wa/demar 1T fieflaz.

WITNESSES:

ATTORNEY Dec. 2, 1941, w L BENDZ 2,265,022

AERIAL PASSENGER TRAMWAY Filed Feb. 18, 1939 2 Sheeis-Sheet 2 WITNESSES:INVENTOR 7%M Wa Memar Z fieflaz.

ATTORNEY Patented Dec. 2, 1941 AERIAL PAS SEN GER TRAMWAY Waldemar I.Bendz, Arlington, Mass, assignor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application February 18, 1939, Serial No. 257,171

13 Claims.

This invention relates to tramway control systems, and is particularlydirected to a system in which a car is moved through a predeterminedpath from one terminal position to a second terminal position, by meansof a traction cable to which power is imparted through a motor drivensheave.

Because of the nature of the drive involving the transmission of powerfrom the sheave to the traction rope, or cable, solely by the frictionbetween the cable and the sheave, there may be a certain amount ofslippage between the sheave and the traction rope. An indicator, that isprovided to show the position of the traveling car, is usually alsodriven from a shaft that is mechanically connected to the sheave.Consequently, when slippage occurs between the sheave and the tractionrope, the position of the indicator for the car will not correspond to,or be synchronous with, the position of the car and the indication givenby the position indicator will therefore be false.

In the tramway system to which my present invention is applied, thepassenger car travels along a supporting cable which is suspendedbetween supports a considerable distance apart. Consequently, the cardoes not assume a definite position either vertically or horizontallywithin limits of position which are sufliciently close to permit theoperation of a limit switch of the track type or so-called hatchwaytype. This is due to the fact that the vertical position of the car isvariable, depending upon the load of the car and the sag of the cable,which may also be variable depending upon temperature as well as weightof the car and passengers. The horizontal position of the car is alsovariable due to wind and the unbalanced loading in the cars.Consequently, the usual form of limit switch of either of the typesmentioned is not applicable to a drive of this type. While limitswitches cannot be properly located to obtain the necessary number ofslow-down points prior to a definite stop for the reasons as namedabove, it happens that the cars are carefully guided during the last fewfeet of travel so as to properly position the car for unloading ofpassengers.

In the present system, I employ a limit switch to be controlled by thecar to aid in correcting the position of the indicator; and also employthe indicator, if desirable, to provide slow-down control for the mainmotor.

The primary object of my invention, therefore, is to provide a systemthat will automatically correct any deviation of the position indicator,when it deviates from a proper position corre sponding to the positionof the car, because of slippage between the sheave and the tractionrope.

In the accompanying drawings,

Figure 1 is a simple operating and control system arranged to operate inaccordance with the principles of my invention;

Fig. 2 is a diagrammatic view showing the general disposition of thetramway system to which my invention has been applied: and

Fig. 3 is a simple operating and control system embodying a modificationof my invention.

As shown in the diagram in Fig. 1 a main power motor I for the tramwaysystem is arranged to be energized from a power circuit 2. The motor Idrives a sheave 3 through appropriate reduction gearing 4. The sheave 3is of the usual grooved pulley form and is arranged to drive a tractioncable or rope 5 by friction. The traction cable 5, as illustrated inthis application, operates substantially as an endless cable, in suchmanner that one portion 6 of the cable moves a tram car 1 in onedirection, while an adjoining portion 8 of the cable will move a secondtram car 9 in the opposite direction.

It will be understood, of course, that instead of an endless cable anequivalent system might be employed in which the two ends of the cablewould be controlled to impart the proper direction of movement to reelin one end of the cable while paying out the other. Also, instead of anendless cable system on which two passenger cars are fastened, anequivalent system might be employed using only one car which is made totravel back and forth between two terminal po sitions. In either systemthe passenger car or cars may be replaced by a device or devices forcarrying freight or other form of material.

Where two cars or devices are used, the system is a double reversibletramway. Where one car is used, the system is a single reversibletramway.

As shown in the drawings, the two tram cars will be alternately movedfrom one of their respective terminal positions to the other of theirrespective terminal positions. In order to provide the reversingmovement to the cable, the motor I, which is shown as a shunt-wounddirect current motor, is reversely energized by reversely connecting thefield Winding II to the main power circuit 2 through either of twoswitches l2 0r Hi. The switches l2 and I3 are, in turn, selectivelycontrolled by a controller switch [4 that is illustrated for simplicityas a single-pole double-throw switch. The armature circuit is i1-lustrated as passing through contact members on either switch l2 or l3so the motor circuit will be opened, as both switches l2 and I3 aredeenergized, when the master switch I4 is thrown to neutral position.

In order to slow down the main motor I as the tram cars l and 9 approachtheir respective terminal positions, the motor circuit is appropriatelycontrolled to reduce the motor speed. In

practice, the system actually employed for that cuit when the motor isto be decelerated, and con-.

versely, to be shorted out of the armature circuit when the motor is tobe accelerated from rest, in a manner and for a purpose that will bedescribed below.

In order to indicate the respective positions of the tram cars 1 and 9,two position indicators l8 and I9 are provided. The position indicatorsare disposed upon threaded nuts 2| and 22 respectively mounted uponthreaded lead screws 23 and 24, that are respectively driven by gears 25and 26. a common driving gear 21 that is connected to the driven element28 of a differential gear mechanism 29. The driving gear 3| of thedifferential mechanism 29 is connected through a suitable gear reduction32 to the shaft 33 upon which the driving sheave 3 is connected.

In order to provide automatic or manual adjusting control of theposition indicators i8 and I9, the differential mechanism 29 is providedwith a driving gear 34 on the housing 35 of the differential mechanism29. The housing 35 supports the two differential idler gears 35 and 31that transmit motion from the driving gear 34 to the driven gear 28 ofthe diiierential mechanism.

In order to rotate the diiferential housing 35' by its gear 34, anauxiliary reversible motor 38 is provided that is disposed to rotate thehousing '35 in either direction through a pinion 39, or to hold thehousing 35 stationary to permit the differential operation of thedifferential mechanism.

When no slippage occurs between the driving sheave 3 and the tractionrope or cable 5, the movement of the traction rope, and, consequent- 1y,of either tram car, will be attended by a corresponding proportionalmovement of the position indicators |8 and I9. The indicators will,therefore, occupy their respective terminal positions'when the tram carsare at their respective terminal positions.

Because of the slippage, however, that occurs between the driving sheave3 and the traction rope 5, due to the tension in the'traction rope,which may be either positive or negative with respect to the torque ofthe driving sheave, the

position indicators will, more often than not, :not always be in acorrect position corresponding to the position of the associated tramcars. In order to correct for such deviation of the position indicatorsfrom their proper positions due to cable slippage on the sheave, twolimit switches 4| and 42 are provided and disposed adjacent the end orterminal'positions of the path of each of the tram cars 11 and'9,respectively, sothat the switches will be operated when the associatedtram car moves to itsultimate posi tion at a selected-terminal. Thelimit switches 4| and 42, as controlled by their respectivetram cars 1and 9, are employed to set up and control the circuit of the auxiliarymotor 38 for the differential mechanism 29.

In order to complete the control of the auxiliary motor 33, two otherauxiliary switches 43 and 44 are provided, and they are disposed at theultimatepositions at selected terminal positions of the two indicatorsl8 and i9.

The gears 25 and 25 are driven by Thus, each tram car and its associatedposition indicator cooperate to control the auxiliary operation.

"Energy for the auxiliary motor 38 is shown as derived from athree-phase supply circuit 45. 'The motor '38 is also provided with afriction solenoid brake 46 of the conventional type, which is releasedwhen its operating coils 41 are energized and which is set by springs,for example, when its operating coils 41 are deenergized.

When no electric power is applied to the auxiliary motor 38, the brake45 is set, and, through the gear connection betweenthe gear pinion 39and the differential housing 35, locks the housing 35 against motion.While this condition exists, the differential acts as a straightone-to-one gear transmission to transmit rotation from the sheave shaft33, through thegear reduction 32, to the driving gear 21 for the gears25 and 26 to the lead screw gears 23 and '24.

When operation of the 'Jtransmisison is attended by no slippage betweenthe sheave and the traction rope, each tram car will reach its terminalposition at the same time as the corresponding position indicatorreaches its terminal position. Under such condition no correction of theposition indicators is required.

When conditions are such, however, that slippage does occur between thesheave and the traction rope, movement of the position indicatorswillnot be proportional to and synchronous with the cable, and each positionindicator will therefore not reach and occupy its correct relativeposition when its associated car reaches the terminal position. In orderto correct for such deviation, the limit switch controlled by each carand the limit switch controlled by the associated position indicator arecooperatively connected, in series, to supply energy from the supplycircuit 45 to the auxiliary motor 38, in the proper direction to rotatethe housing of the differential mechanism, to operate the lead screws 23and 24 ated car 1 when the car is in its terminal position.

The limit switch 42 for the car 9 is similar to limit switch 4|, and isprovided with similar contact members 58 and 59 and a biasing spring 69together with a control pivoted lever 6|, corresponding to the sameelements on limit switch 4|.

A cooperating limit switch 43, that is controlled by the-positionindicator l8 at one terminal position, is also a double contact switchprovided with two contact switches 53 and 54 that are normally biased toclosed position by a spring 55. An operating button 56 is provided to beengaged and depressed by a roller 51 on the position indicator l8 toopen the circuits between the two contact switches 53 and 54.

A limit switch 44, controlled by the position indicator H3 at its otherterminal position, is provided with contacts 63 and 64, a biasing spring65 and an operating push button 66 similar to those provided for thelimit switch 43.

The limit switch 43 is disposed to be operated by the position indicator|8 at the left-hand limit of its travel, and the limit switch 44 islocated to be operated by the roller of the position indicator It! atthe right-hand limit of its travel, at a position corresponding to therelative terminal or limit position of the position indicator l9. Theoperation of the two limit switches 43 and 44 by the position indicator|8 permits the position indicator l9 to be utilized for other controlfunctions.

If no slippage has occurred between the sheave and the traction rope 5,while the car I has been raised from its lower terminal position to itsupper terminal position, the position indicator l8 will move to, and bein, its proper relative terminal position to open limit switch 43 whencar 1 reaches its upper terminal position to close the limit switch 4|.Thus, although the circuit for motor 38 will be set up at the limitswitch 4|, it will be open at the limit switch 43 to keep the circuitopen between the auxiliary motor 38 and its source of supply 45.

If, however, slippage has occurred between the sheave and the cable, dueto an excessive loading of car 9, for example, so that the car 1 willreach its terminal position and close its limit switch 4| beforeposition indicator |8 has been moved to its proper relative terminalposition to open limit switch 43, limit switch 43 will still be closedwhen limit switch 4| is closed by movement of the car 1 to its upperterminal position. Indicator l8 will at that time occupy the dottedposition A adjacent its proper relative terminal position above limitswitch 43.

The energizing circuit is then closed from the supply source 45 throughlimit switch 43 of the position indicator 8, thence through limit switch4| at car I, to the brake coils 41 and to the auxiliary motor 38. Asshown, the third conductor of the supply circuit 45 is connecteddirectly to the motor. Consequently, the brake coils are energized torelease the brake and the auxiliary motor is energized to rotate thecase or housing of the differential mechanism. Since the main motor isnow stationary, the sheave shaft 33 and the transmission unit 32 will beheld stationary, and the rotation of the differential mechanism casewill rotate the lead screws 23 and 24 until the position indicator I8 ismoved to its proper relative terminal position where it will engage andopen the limit switch 43. The circuit to the auxiliary motor willthereupon be opened and. the brake restored to hold the auxiliary motoragainst further rotation.

When the main motor operation is reversed to lower the car "I, and toraise the car 9, the limit switch of car I will be opened, and, when car9 reaches its upper terminal position, limit switch 42 will be closed.Limit switch 42 will cooperate with the position indicator switch 44according to the position of the position indicator when the car 9reaches its upper terminal position.

When the car 9 is in the proper terminal posi tion, the positionindicator will open its limit switch 44, if no slippage has occurred. Ifslippage has occurred, the position indicator will move to position Bwhen car 9 reaches top terminal position. Limit switch 44 will be closedand will cooperate with car limit switch 42 to complete the circuit fromthe auxiliary supply source 45 to the auxiliary motor 38 to energize 7and release the brake 46, and to operate the case or housing 35 of thedifferential mechanism 29. The connections to the auxiliary motor arenow reversed, however, with respect to the connections made through theother set of limit switches, and the direction of operation of theauxiliary motor 38 is now reversed. The lead screws are now operated tomove the indicator I8 from position B to its proper limit position toopen limit switch 44.

Assume, instead, that car 9 is excessively loaded as compared to car 1,thus causing slipping and that car 9 is raised from the full lineposition to the dotted line position, at the latter position closinglimit switch 42. The indicator 8 will have overtravelled to the right oflimit switch 44 to a position C (indicated in dotted lines). Therefore,since both limit switches 42 and 44 are closed, a circuit will becompleted through motor 38 which will efiect a movement of the positionindicator |8 to the right but which movement will be arrested by virtueof the fact that the threads of the lead screws 23 and 24 terminate justbeyond the limit switches 43, 44 and just beyond switches and 86 atwhich positions are located biasing springs 9|, 92, 93 and 94 which urgethe position indicator members in a direction toward the center of thelead screws. Therefore, as soon as the cars are moved in an oppositedirection, that is, as soon as 'car 9 is moved from the dotted lineposition to the full line position, the position indicator 8 will bepropelled to the left to approximately position. A at which time limitswitch 4| will close and owing to the fact that limit switch 43 is alsoclosed, a circuit to motor 38 will be completed thereby efiecting acorrection of the position of indicator l8 (1. e., movement of indicatorl8 to the left until it opens limit switch 43). In the event thatinstead of moving to a position A, the indicator again overtravelsbeyond the limit switch (this time, to the left of limit switch 43) noimmediate correction will be aiforded and none will be had until theposition indicator is stopped somewhere between limit switches A and 13.While this situation does permit inaccuracy of the position indicator,such inaccuracy is very small for one or a few round trips. The em.-bodiment illustrated in Fig. 3, which will be described hereinafter,completely eliminates the above-described errors.

In order to decelerate the motor to permit slow landing of the cars atthe upper terminals, the armature circuit of the main motor is providedwith the three resistors l5, l6 and I! previously referred to. Theseresistors are progressively short-circuited as the cars move away fromterminal position and are progressively inserted into the armaturecircuit as the car approaches and gradually moves into its finalterminal position at the loading terminal.

I show these resistors |5, I6 and H merely to illustrate a simple systemfor establishing a gradual deceleration of the motor. In actual practicea variable voltage direct current system is employed to control themotor speed, but its description would unnecessarily enlarge thisdescription of the operation of that part of the system.

In order to control the insertion and removal of these resistors |5, H5and H into and out of the motor circuit, three short-circuitingcontactors H, 72 and 13 are employed for the respective resistors. Theoperating coils of the contactors ll, '12 and 13 are controlled bysuitable interlocking switches, of which switches I4, I5

gressively open switches I3, I2 and II to deenergize theshort-circuiting contactors and progressively and cumulatively insertthe resistors II, I6 and I5 in the armature circuit of the motor.

Conversely, as the carsrnove away from the upper terminal position, theposition indicator I9 will progressively reset the interlock switches toreenergize'the contactors 'I I, I2 and I3 to progressively short-circuitresistors I5, I6 and II,

.in sequence, to permit the motor speed to gradually increase.

As schematically illustrated, each of the interlock switches I4 to I9,inclusive, is provided with a suitable actuator 80, and a toggle, orovercenter, spring to hold the switch in the position to which it waslast operated.

Each actuator 80, for the interlock switches I to I9 consists of anelement provided with two arms 8| and 82 to be engaged by the roller 83of the position indicator I9. When the roller engages the top arm BI,the switch is forced upwardly; when the roller engages the lower arm 82,the switch is forced downwardly. An overcenter toggle spring 85 isoperated by the actuator 80 and serves to move the actuator and theswitch to the extreme terminal positions of their path of movement, andto hold the switch in open or in closed position to which it has beenmoved.

When the toggle spring is moved by one arm of the actuator to move theactuator to its ex- H treme position in one direction, the other arm forcontrolling movement of the switch to the other direction, is moved intothe path of the roller, to be engaged by the roller when the indicatorreverses and moves back in the opposite direction. The roller 80 engageseither arm of the actuator and moves the switch against the associatedspring, to open or to close the circuits at the contacts of the switch.

When indicator I9 moves from its extreme left v position towards theright, switch I4 is operated to closed position, by the positionindicator I9, to set up the circuits of all three operating coils of thecontactors II, I2 and I3. The circuit for contactor II is completed .andcontactor II operates to shunt resistor I5. As the position indicator I9continues to move, however, it engages the lower arm of the actuator forswitch I5, and moves switch I5 to closed position to close the circuitof th coil of contactor I2 and to set up the circuit for contactor I3.Contactors II and I2 will be held closed to short-circuit resistors I5and I6.

As I the position indicator I9 progressively moves to the right, itsroller will engage the lower arm of the actuator of switch I6 and willoperate switch I6 to closed position to close the circuit of the coil ofcontactor I3. When switch I3 closes, it short circuits resistor II. Themotor will then be energized with full voltage and accelerated tooperating speed. The position indicator I9 ,will continue to move inaccordance with the movement of the tram system.

As the position indicator, I9 approaches th other end of its path oftravel, the switches 'II, I8 and I9 will be similarly operated insequence, and their associated contacts will be opened to deenergizecontactors I3, I2 and I I, sequentially, to progressively insert theresistors II, I6 and I5 .into the circuit of the motor armature.

As shown in Fig. 1, for the purpose of illustration, switch I9 is inclosed position. That is the position switch I9 would occupy just beforethe roller of indicator I9 would engage the'upper arm of the actuator tomove switch I9 to open position. It is also the position that switch I9would occupy immediately upon reclosure, where the indicator I9 wasstarted in operation from its extreme position, at the right, towardsits terminal position at the left.

It will be observed that the actuatorsfor the switches are reverselyarranged in the two terminal groups, so that motion of the indicatortoward either terminal position will open the switches, and motion ofthe indicator from either terminal position will reclose the switches.

By means of such an arrangement, or its equivalent, the speed of themain drivinghmotor may be controlled according to the position of thecar or carsof the system. i V

In addition, the proper relation between the cars or cars of the systemand the position indicators is automatically established and maintainedby the auxiliary motor, which corrects for any deviation during eachcycle of operation.

Fig. 3 illustrates a modification of my invention in which there are twocars, IOI and I02, attached to an endless cable I93. The cable makes oneor more turns around adriving sheave I64 and one of the cars istravelling up hill while the other car is travelling down. 'A drivingmotor I96 drives the sheave IG I through a suitable gear reduction I05.

The passenger cars travelup and down and are brought to a stop atpassenger loading platforms at either end of the trip. An operatorcontrols the movement of the cars and brings them to a proper stop atthe loading platforms. This control of the car movement is manual undernormal circumstances. However, in order to in corporate necessary safetyfeatures itis required that the passenger cars be brought to a normalstop at the proper position at each of the loading platforms regardlessof the efficiency or physical alertness of the operator. In other words,if the operator becomes physically disabled or otherwise inattentive itis necessary to have the cars automatically stopped by the control inorder to prevent an accident.

While there are several safety features incorporated in the control tobring the cars to a safe stop in case the operator fails to properlymanipulate the control it is necessary to make this function automaticwith respect tothe position of the cars. Because of the high speed ofthe cars it is highly desirableto have two or more points of automaticslow-down prior to reaching the final limit position of the cars.

A suitable gearing IE1 is interposed between the shaft of thedrivingsheave and one member of a differential gear I08, another'memberof the differential gear coupled to a screw I99 of the travelling nutlimit-switch. The third member of the differentialgear I08 is directlycoupled to 'a small reversing driving motor III equipped with aspring-setmagnetic-release friction brake I I2. Consequently, if themotor III remains stationary the differential gear will drive directlythrough between the gear reduction I01 and the screw of the travellingnut switch I09. A dog IIO can travel along the screw I09 and operate anyof the various toggle type switch units such as II3-II4 or I23-I28. Whenthe screw of the limit switch is properly aligned with respect to theposition of the passenger cars the dog II travelling on the screw I09should be at position A when the passenger cars are brought to a stop atthe proper place at the loading platforms. At this position of theswitch the dog should engage the switch II 4 so that the poles of theswitches H8 are moved to their open position thereby disconnecting themotor III from the source of power I32-I33I34.

Two track type limit switches H9 and I20 are located so that thepassenger car will close the contact members I2I of switch II9 when thecar I02 is brought to its proper position at the loading platformsillustrated by the dotted lines. Likewise switch I20 closes contactmembers I22 when car IOI reaches the position illustrated by the solidlines.

Assume that car IOI is brought to a proper stop at the upper loadingplatform (illustrated by the full lines) and assume that dog H0 is in anincorrect position as shown due to slippage between the cables andsheaves. Switch I20 thereby closes contact members I22 and a circuit isthen completed from the supply line I3I to lower contact members I 22,conductor I34, upper contact members II8, conductors I35, I36, thence toone terminal of motor III. Another circuit is also completed from supplyline I33 to upper contact members I22, conductor I31, lower contactmembers IIB, conductors I38 and I44 to a second terminal of motor III.The third terminal is directly fed by conductor I32. Assume that due toslipping of the cable on the driving sheave the dog II 0 on the screwI09 stops at position C and, therefore, contact members II 8 are closed.The circuit is then established to energize the motor II I driving thecontrol member of the differential gear I08. Since the sheave I04 is atstandstill and the shaft driven by gearing I01 of the differential gearlocks, rotation of the driving motor III will cause rotation of thescrew I09. In this manner the screw will propel the dog IIO upwardlyuntil switch I I4 opens contact members H8 in order to stop the drivingmotor. The screw has then been corrected to the proper position and hascompensated for slip of the cable I03 with respect to the driving sheaveI04.

Had the error been in the opposite direction the dog may have been movedtoo far by the screw and have assumed such position as illustrated by B.In this case the switch I I4 would close contact members II 1 and opencontact members II8 thereby effecting a reversal of one of the incomingphase lines (I36-I34) and establishing a circuit to the driving motor III in the reverse direction and the screw I09 would be driven in adirection as to propel the dog IIO downwardly. In other words, the finalposition of the dog IIO will be midway between the position AB as shown.

Correction at the opposite limit of travel is made in exactly the sameway by operation of the switch II9 closing the contact members I2I whencar I02 reaches the position illustrated by the dotted lines, completingthe power circuit to switches H and H6. The procedure is exactlyanalogous to that outlined previously.

Switches I23 and I24 are incorporated as a part of the control equipmentfor driving the motor I06 and are the switches which control the finalposition limit and will cause the motor I06 to stop if the dog IIOengages either of.

switches I23 or I24. It is important to note that these latter switchesmust be operated by travel of the dog IIO beyond the position whichoperates the switches II3 and H4, previously discussed. Therefore, whenthe cars are stopped in their proper position by the operator manuallyoperating the control, neither of the switches I 23 and I24 is engagedby the dog IIO. However, if the operator fails to shut ofi the powerdriving motor I06 the dog IIO will operate either switch I23 or I 24which because of their series relationship with relay I43 will effectdeenergization thereof and eifect stopping of the motor I06 and the carswill come to rest slightly beyond the travel which they normally assume.However, this diiferential in travel need only be a few feet and therewould be no danger in such operation.

Switches I25, I26 and I21, I28 are used to slow down the operating speedof driving motor I06 prior to reaching the final limit position. Thereare only two such switches shown, but in actual practice this number maybe four or more. The function of the control would be in case theoperator failed to slow down the motor I06 by operation of the manualcontrol master switch engagement of dog I I0 with switches I26, and I25would deenergize relays MI and I42, successively, thus insertingresistances I39 and I40, successively in the main motor circuit thusslowing down the speed of motor I96 and finally stopping the motor whenthe dog I I0 reached the position B shown on the drawings that is afterswitch I 23 has been actuated. The operation would be similar if thelimit of travel were in the opposite direction in which event switchesI21 and I28 effect operation of relays MI and I42 respectively.

As shown in the drawings, the two tram cars will be alternately movedfrom one of their respective terminal positions to the other of theirrespective terminal positions. In order to provide the reversingmovement to the cable the motor I06 which is shown as a shunt wound,direct current motor, is reversely energized by reversely connecting thefield Winding I50 to the main power circuit through either of the twoswitches I5I or I52. The switches I5I and I52 are, in turn, selectivelycontrolled by a controller switch I55 which is illustrated, forsimplicity, as a single pole double throw switch. The armature circuitis illustrated as passing through contact members on either switch I5Ior I52 so the motor circuit will be opened as both switches I SI and I52are deenergized, when the master switch I55 is thrown to the neutralposition.

In order to decelerate the main motor I06 as the tram cars IOI and I02approach their respective terminal positions the motor circuit isappropriately controlled to reduce the motor speed. In practice, thesystem actually employed for that purpose is a variable voltage directcurrent system, but, for the sake of simplicity, I have illustrated asimple system in which the armature circuit is provided with tworesistors I39 and I40 connected in series relationship and which arearranged to be progressively inserted into the armature circuit bydeenergization of relays MI and I42, respectively.

Since it is necessary in most cases to provide a position indicator forindicating the position of the cars being operated, the equipment used'to: correct the screw of the travelling nut limit switch described abovemay also be used to correct the position of the indicator.

Referring to Figure 3, one method of accomplishing this would be tocouple a gear reducer I29 of the proper ratio to the screw I09 of thetravelling nut switch so as to operate a position indicator 130. Theratio of this gearing would be such that the full scale movement of theindicator would correspond to the movement of the cars for one trip. Theposition indicator may be directly coupled by some means of gearingillustrated or else it may be remotely operated by the conventional'typeof synchcro-tie drive.

My invention is not limited to the details of the'system illustrated,since they may be modiiied to achieve the same result without departingfrom the invention asset forth in the appended claims.

V I claim as my invention:

1. In a tramway system, the combination with a driving motor, a sheavedriven thereby, a traction rope drivenby the sheave to operate a car,and a position indicator also driven by the motor to indicatetheposition of the car, of a differential mechanical connection betweenthe motor and the position indicator to permit operation of the positionindicator independently of the driving sheave to permit readjustment ofthe indicator relative to the sheave to compensate for slipping betweenthe sheave and the traction rope and actuating means including the caritself for initiating said readjustment at terminal positions of saidcar.

2. A system as in claim 1, including an auxiliary motor that is providedto drive or to brake one element of the differential mechanicalconnection, and'switching means directly controlled by the car at aterminal position of its path of travel for controlling the operationand direction of rotation of the auxiliary motor.

3. In a tramway system, in which a motor-operated sheave drives atraction rope to move a car back and forth along a predetermined path,and also drives a travelling nut position indicator, means forautomatically correcting the position of the indicatorfor slip betweenthe traction rope and the sheave, said means comprising athreadedactuator for the travelling nut indi-i cator, a differential mechanicaldriving connection between the sheave and the threaded actuator for theindicator a motor for driving or for holding stationary one element ofthe differentialdriving connection, and a pair of limit switches, onelocated at each end of thepathof travel of the-car and in a position tobe directly operated by the car at each end of its travel, forcontrolling a circuit to the motor for the differential to cause themotor to operate the actuator to shift the indicator, if necessary, tocorrect for slippage between the sheave and the traction rope.

4. In a tramway system, in which a motoroperated sheave drives atraction rope to move a car back and forth along a predeterminedpath-,andalso drives a travelling nut position indicator, means forautomatically. correcting the position of the indicator for slip betweenthe traction rope and the sheave, said means comprising; a threadedactuator for the travelling nut indicator, a 'differential'mechanicaldriving connection betweenthesheave and the threaded actuator forthe'i'ndicatorjamotor-iordrivingpr ing said source through said limitswitches in for holding stationary one'element: of: the differentialdriving; connection, and a; limit switch located at the endof the-path:of traveler. the:

car and in a position'to'be directly operated by the carat theend of;its travel, for: controlling: a circuit to the motor for thedifferential to: cause the motor to operate the actuatorr'to shiitf theindicator; if necessarmto' correct for: slippagebetweenthe sheave. andthe traction rope,

and a limit switch operable-bythe position'imdicator for'opening' thecircuit between the carresponding to car terminal position.

5. In a tramway system, in which a motoroperated sheave drives a.traction rope to move a car back and for-thalong: a" predetermined'ipath; and also drives a travelling nut position indicator, means forautomatically correcting the position of the indicator for slip betweenthe traction rope-and the sheave; said: means 'com' prising a threadedactuator 'forthe travelling:

nut indicator, a differential mechanical driving ;connection betweenthe'sheave and the threaded actuator'for the indicator, amotor fordriving or for holding stationary one element of the dif ferentialdriving connection, a normally open limit switch'closable by the caratxterm'inalposi:

tion, a normally closed limit 1 switch operable by the positionindicator atterrninal positionsfand" means connectingthe limit switchesin series be tween a source of energy and the motor. for the;

differential;

6. In a tramway system, in which amotora operated sheave drives; atraction rope tofimove a 'car back and forth along ai'predeterminedpath, and also drives a travellingnut position indicator, means forautomatically correcting A the position of'the indicator for slipbetween the 1 traction rope and the sheaveQsaid means comprisingathreaded actuator for the vtravelling nut indicator, adifferentia'l'mechanical driving conmotion between the sheave and thethreaded j; actuator for the indicator, a motor for driving or forholding stationary one element of the:

differential driving connection, two normally open limit switches, eachoperable by car-associated means when the car is at corresponding" limitposition'of its path of travel, two normally closed limit switches, eachoperable-by position-lindicator-associated means when theindicator" isat the corresponding limit positionof its path of travel, a source ofenergy, 'an'd means connectseries, respectively, to the motor'for thedifferthe sheave and the traction rope.

7. In atramway system, the combination with a driving motor, asheavedriventhereby, a traction rope driven by the sheave to operate acar,

and a position 'indicator'als'o driven-by themotor' to indicate theposition of the car, of a differential mechanical connection between'themotor and the position indicator to permit'operationiot the positionindicator independently of the driv..

irig sheave to permit readjustment of theindicator relative to the'sheave to compensate for slipping between the sheave and the tractionrope,'and means theoperation of which is initiated by-the car, itself,when at its terminal 5 position for operating the differentialconnection "to readjust the indicator'relative to the' sheave tocompensate for slippage between the rope and the sheave.

In a tramway system, the combination with a driving motor, a sheavedriven thereby, a traction rope driven by the sheave to operate a car,and a position indicator also driven by the motor to indicate theposition of the car, of a differential mechanical connection between themotor and the position indicator to permit operation of the positionindicator independently of the driving sheave to permit readjustment ofthe indicator relative to the sheave to compensate for slipping betweenthe sheave and the traction rope, and means the operation of which isinitiated by the car itself when at its terminal position for operatingthe differential connection to readjust the indicator relative to thesheave to compensate for slippage between the rope and the sheave, areversible means for operating the differential connection to readjustthe indicator relative to the sheave to compensate for slippage betweenthe rope and the sheave and switch means controlled by the positionindicator and by the car to selectively energize the reversible means.

9. In a tramway system, the combination with a driving motor, a sheavedriven thereby, a traction rope driven by the sheave to operate a car,and a position indicator also driven by the motor to indicate theposition of the car, of a differential mechanical connection between themotor and the position indicator to permit opertion of the positionindicator independently of the driving sheave to permit readjustment ofthe indicator relative to the sheave to compensate for slipping betweenthe sheave and the traction rope, an auxiliary reversible motoroperatively connected to drive one element of the differential mechanismother than that connected to the driving motor to operate the mechanismwhen the driving motor is stationary, and means including the car itselffor energizing the auxiliary motor after the driving motor has moved thecar to terminal position, and the driving motor is stationary.

10. In a tramway system, in combination, a car, a traction cable whichhas a portion thereof fastened to said car, a reversible driving motor,a sheave which is driven by said motor in one direction or another,depending upon the direction of rotation of said motor, to effectmovement of said car in one direction or in an opposite direction; amechanical differential gear system which is driven by said motor, acarpositicn indicator which is driven by said motor through saiddifferential gear system, a second motor which also drives through saiddifferential gear system for effecting adjustment of said indicatorindependently of said first-named driving motor, limit switch meanswhich is adapted to be directly actuated by said car at the end of itstravel for controlling said second motor and the position of saidindicator to adjust for errors due to slippage between said sheave andsaid first driving motor.

11. In a tramway system, in combination, a car, a traction cable whichhas a portion thereof fastened to said car, a reversible driving motor,a sheave which is driven by said motor in one direction or another,depending upon the direction of rotation of said motor, to effectmovement of said car in one direction or in an opposite direction; amechanical differential gear system which is driven by said motor, acar-position indicator which is driven by said motor through saiddifferential gear system, a second motor which also drives through saiddifferential gear system for eifecting adjustment of said indicatorindependently of said firstnamed driving motor, a limit switch at theend of the path of travel of said car and which is adapted to beoperated directly by said car to effect completion of a circuit throughsaid second motor to effect movement of said indicator so to compensatefor errors due to slippage between said sheave and said first drivingmotor, a longitudinally reciprocable switch actuating dog which is alsodriven through said mechanical differential gear system, switch means atthe end of the nor ial travel of said dog which is actuated thereby forinterrupting the circuit through said second motor to interrupt thecorrective movement of said indicator.

12. In a tramway system, in combination, a car, a traction cable whichhas a portion thereof fastened to said car, a reversible driving motor,a sheave which is driven by said motor to effect movement of said car inone direction or an opposite direction; a mechanical differential gearsystem which is driven by said motor, a car-pcsition indicator which isdriven by said .iotor through said differential gear system, a secondmotor which also drives through said differential gear system foreffecting adjustment of said indicator independently of said first-nameddriving motor, a longitudinally reciprocable switch actuating dog whichis also driven through said mechanical differential gear system, switchmeans beyond the end of the normal travel of said dog which is actuatedthereby for effecting a slowing down, and upon further movement, astopping of said first motor.

13. In a tramway system, in combination, a car, a traction cable whichhas a portion thereof fastened to said car, a reversible driving motor,a sheave which is driven by said motor to effect movement of said car inone direction or in an opposite direction; a mechanical differentialgear system which is driven by said motor, a car-position indicatorwhich is driven by said motor through said differential gear system, asecond motor which also drives through said differential gear system foreffecting adjustment of said indicator independently of said first-nameddrivin motor, a limit switch at the end of the path of travel of saidcar and which is adapted to be directly operated by said car to effectcompletion of a circuit through said second motor to effect movement ofsaid indicator so as to compensate for errors due to slippage betweensaid sheave and said first driving motor, a longitudinally reciprocableswitch actuating dog which is also driven through said mechanicaldifferential gear system, switch means at the end of the normal travelof said dog which is actuated thereby for interrupting the circuitthrough said second motor to interrupt the corrective movement of saidindicator and a second switch means at the end of the normal travel ofsaid dog, also actuated by said dog for slowing down the speed of saidfirst motor and upon further travel of said dog, effecting stopping ofsaid first motor.

WALDEMAR I. BENDZ.

